{"id":66472,"date":"2026-10-06T17:18:49","date_gmt":"2026-10-06T14:18:49","guid":{"rendered":"https:\/\/wpcalc.com\/en\/?p=66472"},"modified":"2026-10-06T17:18:49","modified_gmt":"2026-10-06T14:18:49","slug":"osmotic-pressure-calculator","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/chemistry\/osmotic-pressure-calculator\/","title":{"rendered":"Osmotic Pressure Calculator"},"content":{"rendered":"<section class=\"not-prose calculator-box\" aria-labelledby=\"calculator-title\"><div class=\"flex items-baseline sm:items-center justify-between gap-2 sm:gap-3\"><div class=\"flex flex-col sm:flex-row sm:items-center gap-2\"><span class=\"icon icon-calculator text-primary-700! text-base! dark:text-primary-300!\" aria-hidden=\"true\"><\/span><h2 id=\"calculator-title\" class=\"text-lg font-display font-bold\">Find the Osmotic Pressure of a Solution<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"66472\" data-favorite-title=\"Osmotic Pressure\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/chemistry\/osmotic-pressure-calculator\/\" data-favorite-excerpt=\"Calculate the osmotic pressure of a solution from its molarity, temperature and the van &#039;t Hoff factor using the van &#039;t Hoff equation \u03c0 = iMRT. Results are shown in atm, kPa, mmHg and psi.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-biology\">\n    <span class=\"icon icon-shape-star-empty\" aria-hidden=\"true\"><\/span>\n  <\/button>\n  <div class=\"calcdash-favorite__tip\" aria-hidden=\"true\">\n   <span class=\"favorite-tooltip\" id=\"favorite-tooltip\"><\/span>\n  <\/div>\n  <span class=\"sr-only\" role=\"status\" id=\"favorite-status\"><\/span>\n<\/div><\/div><form action=\"https:\/\/wpcalc.com\/en\/chemistry\/osmotic-pressure-calculator\/\" method=\"POST\" class=\"calculator\" id=\"calculator-66472\" data-post=\"66472\"><fieldset class=\"fieldset-input is-1\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field has-term\" id=\"input-1\"><label for=\"field-1\">Molarity<\/label><div class=\"term\">M<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><div class=\"field-group\"><input type=\"text\" name=\"molarity\" id=\"field-1\" aria-describedby=\"calc-info-1\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" placeholder=\"e.g. 0.1\" min=\"0\" value=\"0.1\"\/><div class=\"grid grid-cols-1\"><select id=\"field-2\" name=\"unit\" aria-label=\"Unit\"><option value=\"mol_l\" selected>mol\/L<\/option><option value=\"mmol_l\">mmol\/L<\/option><option value=\"umol_l\">\u00b5mol\/L<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><small id=\"calc-info-1\">Molar concentration of the solute<\/small><\/div><div class=\"field has-term\" id=\"input-2\"><label for=\"field-3\">Temperature<\/label><div class=\"term\">T<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><div class=\"field-group\"><input type=\"number\" name=\"temperature\" id=\"field-3\" aria-describedby=\"calc-info-3\" placeholder=\"e.g. 25\" step=\"0.01\" value=\"25\"\/><div class=\"grid grid-cols-1\"><select id=\"field-4\" name=\"unit\" aria-label=\"Unit\"><option value=\"c\" selected>\u00b0C<\/option><option value=\"k\">K<\/option><option value=\"f\">\u00b0F<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><small id=\"calc-info-3\">Temperature of the solution<\/small><\/div><div class=\"field has-term\" id=\"input-3\"><label for=\"field-5\">van &#039;t Hoff Factor<\/label><div class=\"term\">i<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"van_t_hoff_factor\" id=\"field-5\" aria-describedby=\"calc-info-5\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" placeholder=\"e.g. 1\" min=\"0.01\" value=\"1\"\/><small id=\"calc-info-5\">Number of particles the solute dissociates into: 1 for glucose\/sucrose, ~2 for NaCl, ~3 for CaCl\u2082<\/small><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"66472\">Calculate<\/button><button type=\"reset\">Reset<\/button><\/div><div class=\"field is-checkbox hidden!\" id=\"field-auto-calc\"><input type=\"checkbox\" id=\"auto-calc\"><label for=\"auto-calc\">Calculate automatically<\/label><small>If enabled, the result will update automatically when you change any value.<\/small><\/div><div class=\"fieldset-result is-hidden\" aria-labelledby=\"result-title\" aria-live=\"polite\" role=\"region\"> <h3 class=\"result-title bg-gradient-to-r from-primary-50 to-gray-50 dark:from-primary-900 dark:to-gray-800\" id=\"result-title\"><span class=\"icon icon-s-pulse\" aria-hidden=\"true\"><\/span> Osmotic Pressure Results<\/h3><div class=\"result-box\"><div class=\"field-result\" id=\"output-1\"><span class=\"field-title\"><span>Osmotic Pressure<\/span><span class=\"result-term\">\u03c0<\/span><\/span><span class=\"field-value\" id=\"result-1\" data-unit=\"atm\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result\" id=\"output-2\"><span class=\"field-title\"><span>Osmotic Pressure<\/span><\/span><span class=\"field-value\" id=\"result-2\" data-unit=\"kPa\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result\" id=\"output-3\"><span class=\"field-title\"><span>Osmotic Pressure<\/span><\/span><span class=\"field-value\" id=\"result-3\" data-unit=\"mmHg\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><div class=\"field-result\" id=\"output-4\"><span class=\"field-title\"><span>Osmotic Pressure<\/span><\/span><span class=\"field-value\" id=\"result-4\" data-unit=\"psi\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><\/div><div class=\"result-actions\"><button type=\"button\" class=\"copy-link\"><svg viewBox=\"0 0 20 20\" fill=\"currentColor\" aria-hidden=\"true\"><path d=\"M12.232 4.232a2.5 2.5 0 0 1 3.536 3.536l-1.225 1.224a.75.75 0 0 0 1.061 1.06l1.224-1.224a4 4 0 0 0-5.656-5.656l-3 3a4 4 0 0 0 .225 5.865.75.75 0 0 0 .977-1.138 2.5 2.5 0 0 1-.142-3.667l3-3Z\"\/><path d=\"M11.603 7.963a.75.75 0 0 0-.977 1.138 2.5 2.5 0 0 1 .142 3.667l-3 3a2.5 2.5 0 0 1-3.536-3.536l1.225-1.224a.75.75 0 0 0-1.061-1.06l-1.224 1.224a4 4 0 1 0 5.656 5.656l3-3a4 4 0 0 0-.225-5.865Z\"\/><\/svg><span class=\"copy-link__text\">Copy link to this calculation<\/span><\/button><span class=\"sr-only\" role=\"status\" id=\"copy-link-status\"><\/span><\/div><\/div><a href=\"#respond\" class=\"hidden transition-opacity duration-300 opacity-0 w-50 text-sm justify-center items-center gap-2 px-4 py-2 rounded bg-gray-200 text-gray-700 hover:bg-gray-300\" id=\"leave-comment\"><span class=\"icon icon-comments\" aria-hidden=\"true\"><\/span>Leave a Comment<\/a><\/form><\/section><section id=\"calc-reactions\" class=\"not-prose hidden my-12 bg-gradient-to-r from-primary-50 to-gray-50 border border-indigo-100 rounded-xl px-6 py-4 shadow-sm\" data-post=\"66472\" aria-live=\"polite\" aria-labelledby=\"calc-reactions-title\"><p id=\"calc-reactions-title\" class=\"text-sm text-gray-500 text-center mb-2\">How did this result make you feel?<\/p><div role=\"group\" aria-labelledby=\"calc-reactions-title\" class=\"grid grid-cols-3 sm:flex sm:flex-row sm:justify-around gap-4 sm:items-center sm:flex-wrap\"><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"like\"><span class=\"reaction-count\" data-reaction-count=\"like\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude00 <\/span><span class=\"reaction-description font-medium\">Like <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"helpful\"><span class=\"reaction-count\" data-reaction-count=\"helpful\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\udca1 <\/span><span class=\"reaction-description font-medium\">Helpful <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"confused\"><span class=\"reaction-count\" data-reaction-count=\"confused\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude15 <\/span><span class=\"reaction-description font-medium\">Confused <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"disappointed\"><span class=\"reaction-count\" data-reaction-count=\"disappointed\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude1e <\/span><span class=\"reaction-description font-medium\">Disappointed <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"inaccurate\"><span class=\"reaction-count\" data-reaction-count=\"inaccurate\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\u274c <\/span><span class=\"reaction-description font-medium\">Inaccurate <\/span><\/button><\/div><div id=\"reaction-message\" class=\"hidden mt-8 rounded-md border border-primary-100 bg-white\/50 backdrop-blur-sm px-4 py-2 text-sm text-center shadow-sm\"><\/div><\/section><div class=\"calcdash-ad not-prose calcdash-ad--calc_result calcdash-ad--in-article\"><ins class=\"adsbygoogle\" style=\"display:block\" data-ad-client=\"ca-pub-1721569815777345\" data-ad-slot=\"6317458308\" data-ad-layout=\"in-article\" data-ad-format=\"fluid\"><\/ins><script>(adsbygoogle = window.adsbygoogle || []).push({});<\/script><\/div>\n<style id=\"wpcoderpro-inline-1\">.formula-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section class=\"formula-box\" aria-labelledby=\"formula-title\">\r\n\t<div id=\"formula-title\" class=\"not-prose font-display mb-4\"><span class=\"icon icon-formula\" aria-hidden=\"true\"><\/span><h2>Osmotic Pressure Formula<\/h2><\/div>\r\n\t<figure class=\"not-prose formula\">\r\n\t\t<figcaption class=\"formula-title\">Formula<\/figcaption>\r\n\t\t<div class=\"text-base text-gray-800\" id=\"formula\">\n\\[ \\pi = i \\cdot M \\cdot R \\cdot T \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(\\pi\\) \u2014 osmotic pressure (atm)<\/li>\n<li>\\(i\\) \u2014 van 't Hoff factor (number of particles the solute dissociates into)<\/li>\n<li>\\(M\\) \u2014 molar concentration of the solute (mol\/L)<\/li>\n<li>\\(R\\) \u2014 ideal gas constant, \\(0.082057\\ \\text{L\u00b7atm\/(mol\u00b7K)}\\)<\/li>\n<li>\\(T\\) \u2014 absolute temperature (K)<\/li>\n<\/ul>\n<p>This is the van 't Hoff equation: it states that the osmotic pressure of a dilute solution behaves like the pressure of an ideal gas, where the role of gas molecules is played by solute particles.<\/p>\n<p>\r\n<\/section>\n<style id=\"wpcoderpro-inline-459\">.calculation-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section id=\"calculation\" class=\"calculation-box\" aria-labelledby=\"calculation-title\">\r\n\t<div id=\"calculation-title\" class=\"not-prose font-display\"><span class=\"icon icon-unordered-list\" aria-hidden=\"true\"><\/span><h2>Osmotic Pressure \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> a 0.1 mol\/L glucose solution at 25 \u00b0C. Glucose does not dissociate, so \\(i = 1\\).<\/p>\n<p>\\[ T = 25 + 273.15 = 298.15\\ \\text{K} \\]<\/p>\n<p>\\[ \\pi = 1 \\times 0.1 \\times 0.082057 \\times 298.15 = 2.4465\\ \\text{atm} \\]<\/p>\n<p><strong>Result:<\/strong> the osmotic pressure is about 2.4465 atm, which equals 247.9 kPa, 1859.4 mmHg or 35.95 psi.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to Use the Calculator<\/h2>\n<ol>\n<li>Enter the <strong>Molarity<\/strong> of the solute and choose its unit (mol\/L, mmol\/L or \u00b5mol\/L).<\/li>\n<li>Enter the <strong>Temperature<\/strong> of the solution and select \u00b0C, K or \u00b0F. The value is converted to kelvin automatically.<\/li>\n<li>Enter the <strong>van 't Hoff Factor<\/strong>: use 1 for glucose, sucrose or urea; about 2 for NaCl; about 3 for CaCl\u2082.<\/li>\n<li>Read the <strong>Osmotic Pressure<\/strong> in atm, kPa, mmHg or psi from the results panel.<\/li>\n<\/ol>\n<h2>What Is Osmotic Pressure?<\/h2>\n<p>Osmotic pressure is the pressure that must be applied to a solution to prevent pure solvent from flowing into it through a semipermeable membrane. The membrane allows solvent molecules to pass but blocks solute particles, so solvent naturally moves from the dilute side to the concentrated side \u2014 a process called osmosis. Osmotic pressure is simply the force per area needed to stop that flow.<\/p>\n<p>What makes osmotic pressure remarkable is that it depends only on the number of dissolved particles, not on their identity. A 0.1 mol\/L sugar solution and a 0.1 mol\/L protein solution of the same particle count generate the same osmotic pressure. This is why the van 't Hoff equation mirrors the ideal gas law: solute particles bouncing against the membrane behave much like gas molecules hitting container walls.<\/p>\n<p>The concept is essential in biology and medicine. Cell membranes are semipermeable, so the osmotic pressure of blood plasma, intravenous fluids and dialysis solutions must be controlled carefully \u2014 fluids that are isotonic with cells cause no net water movement, while hypertonic or hypotonic solutions cause cells to shrink or swell. In chemistry and engineering, osmotic pressure drives reverse osmosis, the process used to desalinate seawater and purify water by pushing it through a membrane against the osmotic gradient.<\/p>\n<p>When interpreting your result, remember that the van 't Hoff factor multiplies the pressure for electrolytes. A 0.1 mol\/L NaCl solution produces roughly twice the osmotic pressure of a 0.1 mol\/L glucose solution, because each formula unit splits into two ions (Na\u207a and Cl\u207b). If you need to work out how to dilute a stock solution to reach a target concentration, the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/c1v1-c2v2\/\">C1V1 = C2V2 dilution calculator<\/a> is a useful companion tool.<\/p>\n<h2>Choosing the van 't Hoff Factor<\/h2>\n<p>The van 't Hoff factor \\(i\\) counts how many particles one formula unit of solute produces in solution:<\/p>\n<table>\n<thead>\n<tr>\n<th>Solute<\/th>\n<th>Dissociation<\/th>\n<th>\\(i\\) (ideal)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Glucose, sucrose, urea<\/td>\n<td>None<\/td>\n<td>1<\/td>\n<\/tr>\n<tr>\n<td>NaCl, KCl, NaNO\u2083<\/td>\n<td>2 ions<\/td>\n<td>2<\/td>\n<\/tr>\n<tr>\n<td>CaCl\u2082, MgSO\u2084<\/td>\n<td>3 ions<\/td>\n<td>3<\/td>\n<\/tr>\n<tr>\n<td>AlCl\u2083<\/td>\n<td>4 ions<\/td>\n<td>4<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>In real solutions, ion pairing and interionic attractions make the effective \\(i\\) slightly lower than the ideal value, especially at higher concentrations. For example, seawater-strength NaCl has an effective factor closer to 1.8 than 2.<\/p>\n<h2>Assumptions and Limitations<\/h2>\n<ul>\n<li><strong>Ideal, dilute solutions only.<\/strong> The van 't Hoff equation assumes solute particles do not interact. At high concentrations, real osmotic pressure deviates from the predicted value, and the osmotic coefficient must be introduced for accuracy.<\/li>\n<li><strong>Complete dissociation is assumed.<\/strong> The calculator applies the \\(i\\) value you enter directly. For weak electrolytes or concentrated strong electrolytes, enter an experimentally effective factor if you know one.<\/li>\n<li><strong>The solute must not cross the membrane.<\/strong> The calculation describes membranes that are permeable to solvent but impermeable to the solute. If the solute diffuses through (as small molecules do through many biological membranes), no steady osmotic pressure develops.<\/li>\n<li><strong>Temperature matters directly.<\/strong> Osmotic pressure scales linearly with absolute temperature, so heating a solution from 25 \u00b0C to 35 \u00b0C raises its osmotic pressure by about 3%.<\/li>\n<\/ul>\n<p>Since the underlying mathematics is the ideal gas law applied to solute particles, you may also find the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/ideal-gas-law\/\">ideal gas law calculator<\/a> and the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/daltons-law\/\">Dalton's law calculator<\/a> helpful for related pressure calculations, or the <a href=\"https:\/\/wpcalc.com\/en\/chemistry\/combined-gas-law\/\">combined gas law calculator<\/a> for other gas relationships.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Calculate the osmotic pressure of a solution from its molarity, temperature and the van 't Hoff factor using the van 't Hoff equation \u03c0 = iMRT. Results are shown in atm, kPa, mmHg and psi.<\/p>\n","protected":false},"author":3168,"featured_media":0,"comment_status":"open","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[54],"tags":[60],"class_list":["post-66472","post","type-post","status-publish","format-standard","hentry","category-chemistry","tag-biochemistry"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66472","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/users\/3168"}],"replies":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/comments?post=66472"}],"version-history":[{"count":1,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66472\/revisions"}],"predecessor-version":[{"id":66473,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/66472\/revisions\/66473"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=66472"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=66472"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=66472"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}